Conventionally a fuel cell includes a stack of elementary cells within which takes place an electrochemical reaction between two reagents which are introduced continuously. The fuel, such as hydrogen, for fuel cells operating with hydrogen/oxygen mixtures (PEMFC) or with methanol for fuel cells operating with methanol/oxygen mixtures (DMFC), is brought into contact with the anode, while the oxidizer, generally oxygen, is brought into contact with the cathode. The anode and the cathode are separated by an electrolyte, of the ion exchange membrane type. The electrochemical reaction, the energy of which is converted into electrical energy, is divided into two half-reactions:                oxidation of the fuel, taking place at the anode/electrolyte interface producing, in the case of hydrogen fuel cells, protons H+, which will cross the electrolyte towards the cathode, and electrons which join the outer circuit, in order to contribute to the production of electrical energy;        reduction of the oxidizer, taking place at the electrolyte/cathode interface, with production of water, in the case of hydrogen fuel cells.        
The electrochemical reaction takes place at an electrode-membrane-electrode assembly.
The electrode-membrane-electrode assembly is a very thin assembly with a thickness of the order of 1 mm and each electrode is supplied with the combustible gases and oxidizer, for example by means of a fluted plate, a so called bipolar plate.
The ion conducting membrane is generally an organic membrane comprising ionic groups which, in the presence of water allow conduction of the protons produced at the anode by oxidation of hydrogen.
The most used commercial membranes today are membranes marketed under the brands of Nafion®, Flemion®, 3M®, Fumion® and Hyflon Ion® produced on an industrial scale.
In spite of the high attained conductivity values (for example, up to 100 mS/cm), the aforementioned membranes have the following major drawbacks:                they are permeable to alcohols, in particular to methanol, which makes them incompatible with use in DMFC cells;        they cannot be used under dry conditions, which prevents their use at temperatures above 85° C.;        they have high cost.        
The inventors have offered to develop novel copolymers which may be used for forming fuel cell membranes, which may have good proton conductivity compatible with the aforementioned use, which have hydrophobicity for preventing, when they are in the form of a membrane, diffusion of water or alcoholic solvents through the latter and which have thermal stability and chemical inertia.